Carbon nanotubes (CNTs), comprising multiple concentric shells and termed multi-wall carbon nanotubes (MWNTs), were discovered by Iijima in 1991 [Iijima, Nature 1991, 354, 56-58]. Subsequent to this discovery, single-wall carbon nanotubes (SWNTs), comprising single graphene sheets rolled up on themselves to form cylindrical tubes with nanoscale diameters, were synthesized in an arc-discharge process using carbon electrodes doped with transition metals [Iijima et al., Nature 1993, 363, 603-605; and Bethune et al., Nature 1993, 363, 605-607]. These carbon nanotubes (especially SWNTs) possess unique mechanical, electrical, thermal and optical properties, and such properties make them attractive for a wide variety of applications. See Baughman et al., Science, 2002, 297, 787-792.
Whether a pristine SWNT conducts electrons as a quantum wire [Tans et al., Nature 1997, 386, 474; Kong et al., Phys. Rev. Lett. 2001, 87, 106801; Liang et al., Nature 2001, 411, 665] or behaves as an exceptional semiconductor [Tans et al., Nature 1998, 393, 49; Javey et al., Nature 2003, 424, 654; Durkop et al., AIP Conference Proceedings 2002, 633, 242] is determined by its diameter and chiral angle, uniquely indexed with two integers (n,m) [Saito, R.; Dresselhaus, G.; Dresselhaus, M. S. Physical Properties of Carbon Nanotubes; Imperial College Press: London, 1998]. The wide variety of achievable diameters and chiral angles, and their associated properties, make it possible to select tubes of exactly the right kind for optimized performance; however, controlling their (n,m) structure during manufacturing is currently a grand challenge. Although SWNTs are produced with a variety of methods such as arc discharge [Bethune et al., Nature 1993, 363, 605; Journet et al., Nature 1997, 388, 756], laser ablation [Thess et al., Science 1996, 273, 483], and chemical vapor deposition (CVD) [Zhang et al., Appl. Phys. A: Mater. Sci. & Proc. 2002, 74, 325; Cheung et al., J. Phys. Chem. B 2002, 106, 2429; Li et al., J. Phys. Chem. B 2001, 105, 11424; Choi et al., J. Phys. Chem. B 2002, 106, 12361; An et al., J. Am. Chem. Soc. 2002, 124, 13688; Liu et al., MRS Bulletin 2004, 29, 244; Murakami et al., Chem. Phys. Lett. 2004, 385, 298], none is capable of precisely controlling both the tube diameter and chirality [Liu et al., MRS Bulletin 2004, 29, 244]. In the case of CVD, the most frequently studied method of growth, SWNT diameters are often found to correlate strongly with the diameter of the metal particles from which they are nucleated [Zhang et al., Appl. Phys. A: Mater. Sci. & Proc. 2002, 74, 325; Cheung et al., J. Phys. Chem. B 2002, 106, 2429; Li et al., J. Phys. Chem. B 2001, 105, 11424; Choi et al., J. Phys. Chem. B 2002, 106, 12361; An et al., J. Am. Chem. Soc. 2002, 124, 13688]. However, even starting with metal clusters of identical structure, the growths show no specific control over the chiral angles [An et al., J. Am. Chem. Soc. 2002, 124, 13688].
As a result of the foregoing, a method for the continuous growth of SWNTs from existing SWNTs and/or SWNT seeds would be extremely useful, particularly wherein such methods permit growth of SWNTs with diameter and/or chirality that is identical to the SWNT seeds.